Taylor, Stephen James Guy; (1998) Wireless telemetry of forces from femoral replacements in man: system design and implant fixation study. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Massive orthopaedic implants made of Titanium-6A1-4V alloy have been custom made at Stanmore for limb preservation in cases of bone tumour since the method was pioneered in 1949. In this technique, the diseased bone and synovial joint are replaced with a metal prosthesis and plastic bearing surface. In the majority of cases, the hip or knee joint together with part of the associated femur or tibia is replaced, and the prosthesis is spigotted into the intramedullary canal of the remaining bone, traditionally fixed using polymethylmethacrylate bone cement. Amputation, which was previously the usual alternative, is thereby avoided and the patient enjoys good mobility. Despite general success, several problems exist in the medium to long term, of which the most severe is progressive loosening of the prosthesis in the remaining bone, the mechanism of which is not yet fully understood. This thesis describes the development and use of a telemetry system for measurement of forces acting upon massive orthopaedic implants, in man, in order to determine the load distribution throughout the prosthesis during routine activities and the way in which this progresses with time. The telemetry system comprises; the implanted instrumented prosthesis, mechanically modified to enclose strain gauges and electronics, an inductive power supply / telemeter, and equipment for data logging and display using a portable computer. When measurements are not being taken, there is nothing visually to distinguish the instrumented subject from any other. The main operational features of this system are: permanently implanted hermetically sealed instrumentation, power induction and data telemetry using the same pair of coils, no trailing cables from the patient during measurements, and real time data logging and display. Details of the aims and methodology for two generations of instrumented prosthesis are given, and results from a 2 year follow-up reported.

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